1. Field of the Invention
The present invention relates to a structure for mounting the same type of camshafts on different types of cylinder heads.
2. Description of the Prior Art
Sometimes there is a requirement to reverse access of an intake/exhaust system to an engine from a left side to a right side or from a right side to a left side with respect to a longitudinal axis of the engine without changing the basic engine design including a cylinder bore arrangement and a camshaft drive structure. Such a requirement arises, for example, when an engine for a right steering wheel vehicle is modified for installation in a left steering wheel vehicle, and both engines are assembled on the same engine assembly line.
FIG. 7 illustrates one example of the prior art methods for reversing an access of an intake/exhaust system to a cylinder head between two types of cylinder heads. In performing the reversal, the order of the camshaft drive portion X of the engine and the cylinder portion Y can not be reversed in the longitudinal direction because that would make it impossible to drive the camshaft from the same end of the engine and to mount the engine in a vehicle. Therefore, only the order of arrangement of the intake valves IN and exhaust valves EX for each cylinder is reversed, relative to the longitudinal direction of the engine, but without changing the centerline locations B of each cylinder bore and the locations of the camshaft sprockets S' in the longitudinal direction of the engine.
However, there are two problems with the above-described reversal of the access of the intake valve/exhaust valve arrangement. One problem is that the same type of camshafts can not be used with the two, different types of cylinder heads, and another problem is that the same engine assembly line can not be used for the two engine arrangements. The reasons why such common uses are impossible will be discussed below in more detail.
As illustrated in FIG. 7, in the two types of cylinder heads having intake valve/exhaust valve arrangement orders reversed with respect to each other, the location of each cam N1 of one type of engine A1' and the location of each corresponding cam N2 of the other type of engine A2' are staggered relative to each other by an amount delta (.delta.), while the locations of the thrust planes F1' formed at opposite ends of the thrust bearing housing and the location of the camshaft drive sprocket S' of one type of engine A1' coincide with the respective locations of the thrust planes F2' and the camshaft drive sprocket S' of the other type of engine A2' in the longitudinal direction of the engines. As a result, a distance P between the center of the thrust bearing and the center of a radial bearing located adjacent to the thrust bearing, of one type of engine A1', is smaller than a distance P' between the thrust bearing center and the adjacent radial bearing center of the other type of engine A2' by the amount delta. This means that camshafts C1 and C2 mounted on the two types of cylinder heads A1' and A2', respectively, must have different lengths between the thrust flanges and the adjacent cam journals and that camshafts manufactured on the same camshaft manufacturing line and having the same contour can not be used in common with the two types of cylinder heads.
Further, because a distance between each tapped hole, denoted with mark "x" in FIG. 7, and a reference plane used as a base plane in tapping, such as the thrust plane of the thrust bearing housing or the engine end plane, of one type of engine is different by the amount delta from a corresponding distance between each tapped hole and a corresponding reference plane of the other type of engine, the same tapping equipment setup using the same reference plane can not be used in assembly of the camshafts C1 and C2 on the two types of cylinder heads A1' and A2'. Therefore, the same engine assembly line can not be used for assembly of the two types of engines.